Question

What serves as the counterfactual comparison in a time series regression analysis?

Answer 1

Interrupted time-series analysis (ITSA) is a popular evaluation methodology in which a single treatment unit's

outcome is studied over time and the intervention is expected to "interrupt" the level and/or trend of the outcome,

subsequent to its introduction.Interrupted time series (ITS) analysis is a valuable study design for evaluating the

effectiveness of population-level health interventions that have been implemented at a clearly defined point in time.

It is increasingly being used to evaluate the effectiveness of interventions ranging from clinical therapy to national

public health legislation. When ITSA is implemented without a comparison group, the internal validity may be quite poor.

Therefore, adding a comparable control group to serve as the counterfactual is always preferred.